This invention relates generally to communication systems and more particularly to internetworking within such communication systems.
Communication networks are known to include a plurality of switches that transport user data (e.g. voice, text, video, etc.) between calling parties and called parties. The user data can be transported using any one of a plurality of standardized data transport protocols. Such transport protocols include frame relay, asynchronous transfer mode (ATM), internet protocol (IP), etc. In addition, the switches transport system data that contains information regarding the connections currently being supported. For example, the system data may include congestion information, frame information, packet information, etc.
As is further known, congestion information relayed in communication networks is used to inform switches upstream and downstream that a switch or port is congested, which indicates that the congested switch or port is overloaded and may be causing undesirable delays. When an end-point source switch, or port, receives the congestion information, the port attempts to reduce its transmission rate to the congested node, thus allowing the congested switch to reduce or contain the overload condition. The congestion information is network service dependent, or data transport protocol dependent. In ATM systems, congestion can be indicated between sources and destinations (which include virtual source/virtual destination blocks) through the use of resource management (RM) and backward resource management (BRM) cells that carry congestion indications. The typical means for communicating congestion states in frame relay systems is through the use of the forward and backward explicit congestion notification bits (FECN and BECN, respectively) in data layer frames, or through the use of a consolidated link layer management (CLLM) congestion indication in a management layer frame.
When the communication network includes both frame relay and ATM switches (i.e. frame relay and ATM internetworking), protocol dependent congestion information is typically only understood and processed by switches of like protocol and passed as data traffic by switches of dissimilar protocols. For example, if a prior art ATM switch is upstream from a congested frame relay node, the prior art ATM switch would typically not recognize congestion information from the frame relay switch and would continue to provide data to the frame relay switch as before, possibly compounding the congested condition.
In some systems, a limited amount of congestion information is communicated between portions of the network utilizing differing protocols. However, the mapping of congestion information that occurs between ATM and frame relay protocols are inadequate in terms of their ability to aid in the control of congestion in the network.
Therefore, a need exists for a more effective method and apparatus for controlling data congestion in frame relay/ATM internetworking systems that allows for better communication of congestion states between switches of different protocols.